Vapour phase oxidation



United States Patent ()fiice 3,350,171 Patented Get. 31, 1967 3,350,171VAPOUR PHASE OXIDATION Alan Edward Callow, Normanby, Middlesbrough, andWilliam Hughes and James Dennis Groves, Fairfield, Stocktou-on-Tees,England, assignors to British Titan Products Company Limited, Durham,England, a company of England Continuation of application Ser. No.774,736, Nov. 18, 1958. This application Jan 20, 1964, Ser. No. 338,982

16 Claims. (Cl. 23202) This is a continuation .of co-pending US.application Ser. No. 774,736, filed on Nov. 18, 1958, and now forfeited.This invention relates to the vapour phase oxidation of titaniumtetrachloride and of other halides which react with oxygen under highlyexothermic conditions. It is known that when titanium tetrachloridereacts with oxygen, heat of reaction is evolved which would sufnce, ifeffectively used, to maintain the reaction at a suitable temperature,within the range of, say, 800 to 1200 C., with the product gases issuingfrom the reaction chamber at that temperature.

Many processes have been described for the manufacture of titanium oxidefrom titanium tetrachloride by oxidation with oxygen oroxygen-containing gases. Such processes include the admission oftitanium tetrachloride and oxygen gases into an empty chamber, throughburners of various designs, but in all these cases, auxiliary heatinghas been necessary and usually accomplished by preheating the gases orby supplying heat through the chamber wall, or by combustion of fuelsWithin the chamber. Such auxiliary heating was not required in order tomaintain the temperature of reaction but only to cause ignition of thereactants by raising their temperature. The excess heat generated by thereaction was not used for pre-heating the gases. Therefore the auxiliaryheat was super-added to the reaction heat, thus Wasting heat and leadingto an unnecessarily and undesirably high reaction temperature.

In a recent development, however, the vapour phase oxidation of titaniumtetrachloride has been conducted in a bed of inert material. Accordingto this type of process the bed material, initially pre-heated, servesto heat up the reactants to the reaction temperature whereupon the heatof reaction liberated in consequence of the reaction is transmitted tothe bed material. Thus, by the turbulent conditions existing in a fluidbed operation the heat of reaction can be utilised to pre-heat thereactants by virtue of the solid inert material constituting the bed.The process has certain disadvantages, particularly a tendency for themetal oxide reaction product to precipitate upon and adhere to the Solidinert bed material. It will be seen that there has been lacking a meansfor transmitting the heat of reaction to the reactants without theassistance of solid surfaces.

In the process, already mentioned, where cold reactant gases are ledinto a preheated empty chamber, it will be appreciated that the coldgases entering, for instance, via a burner at one end .of the chamber,will tend to cool the chamber in that locality and must thereforeproceed through the chamber until they attain the temperature of thereaction. The heat then evolved will in turn be used to pre-heat furthercold gases progressing through the chamber, but the heat zone will tendto move farther away from the point of gas entry until such zone reachesthe furthest end of the chamber when, failing a supply of continuedauxiliary heat, the chamber as a whole will become too cold for reactionto be possible anywhere therein.

The present invention is an improvement in a vapour phase oxidationprocess of the kind in which titanium tetrachloride, or other metallichalide or rnetalloid halide (such as a silicon halide) which reactsexothermically with oxygen or oxygen-containing gas, is reacted withsuch gas in an empty chamber, i.e. a chamber with remote Walls andsubstantially without extraneous solid surfaces.

The improvement according to the invention is characterised in that theadmission into the chamber of the reactants, i.e. halide vapour andoxygen or oxygen-containing gases, and the course of travel imposed onthe gaseous reaction products are such that with the return of asubstantial part of the reaction gases, said reaction products associatewith the reactants and thereby raise their temperature to the level thatis necessary to maintain the reaction. The process may be carried out byadmitting the reactants into the chamber with such kinetic energy that aturbulent flow thereof is created in the chamber causing an entrainmentwith the reactants of a substantial part of the gaseous reactionproducts.

It has been found that if the halide and the oxidising gas are admittedseparately or in admixture into an empty pre-heated reaction chamber ofsuflicient size and under turbulent conditions, the gas stream willexpand seemingly in the form of a cone or like divergent shape. Thisaction has the effect of producing a condition which causes a change ofdirection of flow of the gases so that a substantial part thereoftravels back towards the point of entry. We refer hereinafter to thiseffect as being in the nature of a recirculation or recycling, but we donot wish to be limited by putting forward this particular conception ofthe effect in question.

The effect is particularly pronounced if one or both of the reactants ingaseous form is or are introduced into the reaction chamber through anorifice or nozzle which promotes high velocity and turbulence, becausethe reactants will then tend to entrain the surrounding gas veryrapidly. The mixing with this surrounding gas, consisting mainly of thehot products of reaction, serves to raise the temperature of theincoming gases to reaction-point very rapidly. Accordingly, there isobtained a relatively large volume of product gas (and possiblyentrained solid product) which, after leaving the main reaction zone, ispartially recycled in a continuous manner to mix with the incomingreactants. To be effective, this volume of hot recycled gas must besufiicient to heat the cold reactants to a temperature at which theywill react. In the case of titanium tetrachloride and oxygen, it hasbeen found sufficient, in order to effect reaction, to recycle fiveparts by Weight of the mixed products of reaction to one part by weightof the cold reactants introduced into the chamber. Although in somereactions the desired recirculation might be effected by mechanicalmeans such as by means of a fan, this would be impracticable inreactions such as those now under consideration in which at least one ofthe hot products, e.g. chlorine, is so corrosive. The present inventionobviates recourse to mechanical devices by providing the enteringreactants with a high kinetic energy which will bring about the requiredrecirculation and association of a substantial part of the reactiongases with the reactants.

To effect this recirculation, either or both of the reaction gases is orare fed to a jet, nozzle or other inlet of restricted cross-sectionalarea under such pressure as to produce the required velocity. Normally,this pressure will not need to be greater than 8 lbs. per square inch.Although higher pressures may be used, such a variation is normallyuneconomical. Lower pressure may also suffice but it is essential thatReynolds number of the gas or vapour at the inlet should be in excess of50,000 and Reynolds number N P i where N =Reynolds number and isdimensionless W=the flowrate of fiuid at the inlet (lbs/second) P=thelength of wetted perimeter (feet) ,u=the viscosity of fluid underupstream conditions (lbs./

feet per second) The viscosities for titanium tetrachloride vapour andoxygen used for calculation are as follows:

TiOh Vapour 01 T., C. Viscosity (cp.) T C Viscosity (cp.)

136 1 20x10 20 2. 02 1o 150 1 24x10 100 2. 37x10- 200 1 39Xl0 150 2. 5910 250 1 51 (l0 200 2. 80x10 300 1 67x10 With a burner, as per Example2, having a central orifice in. diameter and titanium tetrachloridevapour admitted at 150 C., the Reynolds number according to the above iscalculated as follows- P Wetted perimeter of a =Viseosity TiCl, vapourat 150C.

=1.24 IO- X 6.73 X

=8.34= 1O' lbs/ft. sec.

The oxygen at a temperature of 160 C. flows through the annulus of saidburner, i.e. between walls having internal diameters of Va in. and W in.respectively and the following is a calculation of its flow number-Wetted perimeter 1r( Z4, 0.375 ft.

It is also important that the reaction chamber into which the reactantsare led at high velocity should be sufficiently large so as not toimpede the recirculatory flow of the hot product gas. Thus, for example,where a circular orifice is centrally-disposed in a cylindrical reactionchamber, the diameter or mean width of said chamber should not be lessthan 20 times, preferably at least 30 times, the diameter of the gasinlet orifice or orifices delivering gas at high velocity. Where theinlet is a circular orifice disposed centrally in a cylindrical chamber,the diameter of the chamber in feet would not normally be greater than0.25 times the square root of w where w is the rate of gas flow throughthe orifice in lbs/hr.

It will be apparent that the desired recirculation may be encouraged byremoving the final product stream from the chamber in the generalneighborhood of the point at which the reactants are introduced, therebycausing a natural reversing flow within the chamber.

There is a wide range of metallic halides, or halides of elements suchas silicon, e.g. those of titanium, aluminum, niobium, iron, chromium,zirconium, vanadium, tin and uranium, or mixtures thereof, present asthe chloride, bromide or iodide, which may be oxidised by means of theprocess of this invention. Normally, however, the chloride is the halidepreferred since it is more economic and readily available.

As indicated above, it is essential that a halide be selected which, byrecirculation under the conditions described generally herein, willenable reaction to be effected without dependence upon auxiliaryheating, other than as will be indicated below, where heat is requiredto convert such halide into vapour or for initially preheating thefurnace chamber.

Normally, the various halides will be caused to react with oxygen, sinceby this means the heat loss is minimised through the absence of diluentgases. Further, the products of oxidation will be richer in halogen andhence more economically recoverable. On the other hand, the use ofoxygen-containing gases, such as air, is not precluded providing thereis adequate heat of reaction to maintain the reaction conditionsessential to the invention.

The reactants may be premixed before passing through the constrictivegas inlet into the chamber or they may be introduced separately. In thelatter instance, one or both is introduced under high velocityconditions.

The reactants are introduced in the form of gas or vapour, so that whereone or more of them exists in the condensed phase under normalatmospheric conditions it or they should be vapourised by pre-heatingbefore feeding, and maintained above saturation-point on entering thenozzle or orifice serving as gas inlet to the reaction chamber. Furtherpre-heating is however, unnecessary. It will be appreciated that, sincecertain halides may not be readily volatilised at relatively lowtemperatures and the present invention is concerned primarily with suchhalides which are volatisable at only moderately high temperatures,preferably below 600 C. there will be preheating to the extent requiredfor volatisation but not to the extent, as in prior processes, forsupplying heat to maintain the reaction in an empty chamber. Theinvention does not contemplate pre-heating to temperatures far in excessof the normal boiling point of the particular halide.

When starting the process, ignition of the gases must be initiated.Pre-heating of the chamber might be considered suitable for suchpurpose, but in practice this may necessitate temperatures in thereaction chamber higher than is desirable and occasionally may presentother difiiculties. It has been found more convenient to initiate theprocess by using an auxiliary flame such as that which is produced bythe combustion of fuel gas, e.g. coal gas, either in oxygen or in air.By this means, once the circulation is established, i.e. within a periodof seconds, this auxiliary flame can be removed and the processthereafter made self-sustaining and continuous. Obviously, however, ifthe reaction should cease for any reason the auxiliary burner would haveto be used again in order to re-initiate the reaction.

From the foregoing description, it will be apparent the process of theinvention involves the use of sizeable apparatus adequate, for instance,to produce at least one ton of Ti0 per day: hence a reaction chambernormally constructed from chlorine-resisting brickwork, suitably backedby insulating brick and contained usually within a steel shell, will benecessitated. Such plant is normally heat-resistant and by this meansunnecessary losses of heat to the surroundings, such as would occur on asmall experimental scale, are obviated.

The conditions, particularly with respect to temperature, preferred inconnection with the oxidation of various metallic halides, or halides ofmetalloids such as silicon, may vary considerably. Thus, in the case ofthe vapour phase oxidation of titanium tetrachloride, the normaltemperature range over which the oxidation may be conducted is from 800to 1200 C. and preferably between 900 and 1100 C.

In the operation of the process for vapour phase oxidation of titaniumtetrachloride, it has been found that the particle size of the titaniumoxide may be controlled by suitable additions of water vapour to thereaction mixture and, where the reactants are added separately, it ispreferably admitted admixed with oxygen-containing gases. It has alsobeen found that the particle size may be modified by additions of smallproportions of silicon tetrachloride, preferably premixed as vapour withthe titanium tetrachloride vapour.

The following examples, described With reference to the accompanyingdrawings, are given for the purpose of illustrating the invention:

Example 1 The reactor, shown diagrammatically in FIGURE 1 of thedrawings, consists of a vertical cylindrical chamber 1 having aninternal diameter of 18" and a height of 11 ft., the inner lining 2,showing plain hachured, consisting of high temperature refractorychlorine-resisting brickwork 11" thick, which is in turn surrounded byan outer insulating brickwork 3, shown cross hachured, 4 /2" thick, thewhole being supported in a steel shell 4, with openings about which arewelded collars 5 and 6 terminat ing with flanges 7 and 8 to correspondto the top and bottom of the reactor respectively. The top opening ofthe cylinder is suitably sealed by a plate 9 with a heat insulatingbrick 9a attached to the underside serving to neatly fit inside thesteel collar 5. Through this seal is inserted the main burner- 10 bywhich the reactants are fed, the titanium tetrachloride via conduit 11and the oxygen via conduit 12. This main burner extends to a depth of 6ft. inside and along the axis of the chamber, i.e. to a point 13.Through the seal there passes also a refractory ducting 14 by which theproducts of reaction are removed. The bottom of the reaction chamber issuitably sealed by a plate 15 having surmounted thereon an insulatingbrick 16, nine inches thick, which neatly fits into the collar 6.Through this plate 15 and brick 16, axially, with respect to thechamber, i.e. through opening 17, there is inserted a small static gaspoker 18 by which coal gas via conduit 19 and air or oxygen via conduit20 are fed to the chamber. The main burner 10 is shown in more detail inFIGURE 2. It consists of a stainless steel metal tube 31, 2 /2" internaldiameter, with flange 32 for affixture to the top of the furnace, thetube being terminated at the outer feed end by a flange 33 to whichthere is affixed the titanium tetrachloride inlet 34. At this end of theburner is an inlet 35 for admission of the oxygen or oxidising gasstream. The burner tube is terminated at the other end, i.e. at thepoint of entry 36 of the gases into the chamber, by a square-edgednozzle 37 /1" diameter), the burner tube from the flange 32 to the end36 being surrounded by high temperature lagging 38 approximately 1"thick, sealed with a silicate cement.

The reaction chamber, with the main burner temporarily removed, has amobile gas poker inserted through the hole normally occupied by the mainburner and by means of this mobile burner, the reaction chamber israised by the admission of coal gas and air to a temperature of 1100 C.At this point, the small static gas poker 18 is lighted and the mobilepoker removed and replaced by the main burner as described.

Gaseous titanium tetrachloride, at a temperature of 150 C., and at therate of 8 lbs. per minute, is thereafter fed through the inlet 34, shownin FIGURE 2, and at the same time, oxygen is fed through the inlet 35 ata temperature of 170 C. and at the rate of 2 lbs. per minute. As soon aschlorine is detectable in the exit duct 14 (FIGURE 1), the static burneris extinguished and the reaction is allowed to proceed for a period ofminutes, during which time a temperature of 10501100 C. is maintainedwithin the reactor. The products of reaction discharge via the duct 14.

Samples taken during the run indicate that the combustion of thetitanium tetrachloride is substantially complete and the solid product,which is subsequently removed from the gases, contains 99% TiO and has amean particle size of 2-5 microns.

Example 2 The reaction chamber is similar to that described in Example 1but in this case the main burner is of a construction indicated inFIGURE 3, to permit introduction of the reactants separately into thereaction chamber in the manner of a concentric tube burner. The burnerconsists of a stainless steel metal tube 41, 2 /2" diameter, constructedto extend 6 ft. into the chamber and terminating within the chamber, ina As" diameter nozzle 42 and sealed externally by means of plate 43aflixed to the flange 44. Into the side of this tube is an inlet 45 forthe oxygen supply. Fitted through the end plate 43 is a ducting 46terminating at flange 47 for admission of the titanium tetrachloride.This stainless steel metal ducting extends to the point of entry ofgases into the reaction chamber, i.e. to the point 48 and having adiameter at this point of thus permitting the entry of titaniumtetrachloride within the concentric stream of oxygen at this point. Thisburner projects into the furnace to the extent of 6 ft., being aflixedto the chamber by means of the flange 50. The whole of the outer surfaceof the burner, i.e. from the flange 50 to the end 42 is lined with hightemperature lagging 1" thick 51, sealed with a silicate cement.

The chamber is pre-heated as in Example 1, using a mobile gas pokerinserted in the hole through which the main burner is normally affixed.With the small static gas poker lighted, the main burner is substitutedfor the mobile gas burner and titanium tetrachloride is admitted at atemperature of C. and at the rate of 8 lbs. per minute. At the sametime, oxygen containing 1.3% by weight water vapour is admitted via tube45 at the rate of 2 lbs. per minute. As soon as reaction is initiated,the small static gas poker is extinguished and reaction allowed tocontinue for a period of 90 minutes during which a temperature of10504100 C. ismaintained by the reaction.

Samples indicate that reaction is substantially complete and thetitanium oxide reaction product contains 99% TiO and has a mean particlesize of 0.6 micron.

Example 3 The reaction chamber 61 is constructed as depicted in FIGURE 4and differs from the apparatus used in the previous examples, mainly inthat the reactants are admitted from the bottom instead of the top ofthe chamber. It consists in the main of a vertical cylindrical vessel 11ft. high, the upper section, for a depth of 7 ft., having a diameter of18", the lower section tapering to 12" diameter at the base. The vesselis lined with high temperature refractory chlorine-resisting brickwork11" thick, shown plain hachured 62, surrounded by a lining of 4 /2"thick insulating brickwork, shown cross-hachured 63, the whole containedin a steel shell 64. The opening at the top of the furnace is sealed ata flanged end 65 on which is mounted a plate 66 carrying on theunderside a 9" thick insulating brick seal 67. Through the brick seal isa port 68 which is axial with the furnace. Into this port is inserted astatic gas poker 69 by which coal gas via conduit 70 and oxygen viaconduit 71 can be fed for igniting the flame. To the base of the furnaceis a T-piece construction 72 suitably lined with 6" thick refractoryconcrete 73. By means of this T-piece the exit gases are removed via theopening 74. The bottom end of the T- piece is closed by a plate 75supporting an insulated brick 76 which neatly fits through the collar77. Through the brick 76 is normally inserted the main burner 78 whichextends to a point halfway up the furnace and is fed with titaniumtetrachloride via conduit 80 and oxygen via conduit 81, the burner beingaifixed by flanges 82. The main burner 78 is constructed as described inExample 2, i.e. it is a concentric burner as depicted in FIGURE 3.

To pre-heat the reaction chamber the main burner 78 is temporarilyremoved and replaced by a mobile poker fed with coal gas and air and thereaction chamber is pre-heated by this ignited poker to a temperature1100 C. At this stage, the static gas poker is lighted and the mobilepoker removed and replaced by the recirculation burner.

Referring to FIGURE 3, gaseous titanium tetrachloride containing 4% byweight silicon tetrachloride is admitted at a temperature of 150 C. andat the rate of 8 lbs. per minute via the ducting 47; at the same time,oxygen containing 1.3% by weight moisture is admitted at the rate of 2lbs. per minute via the ducting 45. As soon as chlorine is detected inthe exit gas, the small static gas poker 69 (FIGURE 4) is extinguished.The heat of reaction maintains the temperature of the furnace between10501100' C. and the titanium oxide product of reaction is separated andexamined.

It is found, operating in this way, that the conversion of the chloridesto solid oxides is substantially complete, the particle size of thesolids being about 0.4 ,u.

Example 4 The equipment as described in Example 3 (that is the burner,as illustrated in FIGURE 3, and reaction chamber as illustrated inFIGURE 4) were used to carry out the oxidation of silicon tetrachloride,as follows:

After pre-heating the reactor as described in Example 3, and while stillmaintaining the gas flame through inlet 69 (FIGURE 4), a stream of 4.65lbs./min., of silicon tetrachloride vapour, at a temperature of 120 C.was introduced into the reaction chamber, through tube 46, (FIGURE 3) ofburner tube 78 (FIGURE 4) and at the same time, a stream of 2.36lbs/min. of oxygen at a temperature of 100 C. was introduced throughducting 45 (FIGURE 3). The oxygen stream contained water vapoursuflicient to react with 2% of the silicon tetrachloride.

After the lapse of 3 minutes, the gas and air streams entering throughports 70 and 71, were stopped, and the reaction-of the silicontetrachloride with oxygen continued in the furnace chamber, eventuallymaintaining a temperature therein of 1020 C. More than 99.5% of thesilicon tetrachloride was reacted in this manner to form a pure silicondioxide with a mean particle size of about 15 millimicrons.

Example 5 The equipment as described in Example 3, (that is the burner,as illustrated in FIGURE 3, and reaction chamber as illustrated inFIGURE 4) were used to carry out the oxidation of ferric chloride asfollows:

The reactor (FIGURE 4) was preheated to a temperature of 900 C. by meansof gas and air burning at the burner 69. When this temperature had beenreached, a stream of 2.67 lbs/min. of oxygen at a temperature of 100 C.was fed into the reactor by tube 45, of the burner illustrated in FIGURE3. Ferric chloride vapour containing 3% by volume of free chlorine wasthen introduced at a temperature of 350 C. through the tube 46 of theburner illustrated in FIGURE 3; this ferric chloride vapour was producedby electric heating of a melt containing ferric and sodium chlorides,and was admitted to the tube 46 at a rate of 14.3 lbs/min. 5 minutesafter starting the flow of ferric chloride vapour, the flow of gas andair to ports 70 and 71 were shut off, whereupon the ferric chloridevapour continued to react with the oxygen, the heat of reactionsuflicing to maintain a temperature of 700750 C. in the reactionchamber. Under these conditions, approximately of the ferric chloridewas converted to ferric oxide of particle size about 2-3 mi- CI'OI'IS.

FIGURE 5 of the accompanying drawings illustrates very diagrammaticallya typical way in which the reactants and reaction products will flow inthe reaction chamber when operated according to the foregoing examples.Example 3 is taken for the purpose of illustration. It will be seen thatthe reactants emerge from the nozzle in a forceful divergent stream andintermingle with reaction products which recirculate back into thereaction zone, whereby the incoming reactants are quickly heated toreaction temperature.

It will be seen from the more particular description given in theforegoing examples illustrating the performance of the process of theinvention that the discharge of the gaseous reaction products takesplace at the same end of the reaction chamber as that where thereactants are admitted. This arrangement in conjunction with the highkinetic energy of the incoming reactants produces, as has been shown,the desired return flow of the reaction products and the entrainment andassociation of a substantial part thereof with the incoming reactants.However, other arrangements may be used whereby the desired result isobtained. For instance the reaction products, or a substantial partthereof, may be delivered at a point remote from Where the reactants areadmitted, from the chamber into a duct leading back into the chamber ata point in the vicinity of the admission of the reactants. The latter,due to their high velocity flow exert suction to draw the reactionproducts through the duct. In this case there may be a discharge exitfrom the chamber at a point remote from the admission of the reactantsso that a part of the reaction products will be continuously dischargedwhilst another part is being returned through the duct to be broughtinto intimate association with the incoming reactants.

What we claim is:

1. In a process for preparing a metallic oxide by the reaction of oxygenwith at least one oxidizable, volatile,

a metallic halide selected from the group consisting of chlorides,bromides, and iodides, the improvement which comprises introducing theoxygen and metallic halide reactants into a reaction zone which is at atemperature at which said reactants will react, at least one of saidreactants being introduced into the zone at a Reynolds number of atleast 50,000 and recovering the resulting oxide, said Reynolds numberbeing calculable as the ratio, in consistent units, of four times therate of fluid flow at the reaction zone inlet to the product of thelength of the inside perimeter of said inlet and the fluid viscosityunder the conditions upstream of said inlet.

2. The process of claim 1 wherein the temperature of the oxygen andmetallic halide when introduced into the reaction zone is such that amixture thereof does not form said metal oxide.

3. In a process for preparing metallic oxide by reacting an oxygencontaining reactant with at least one oxidizable, volatile, metallichalide reactant in which the halide portion of said metallic halidereactant is selected from the group consisting of chloride, bromide andiodide and wherein said reaction is conducted within a reaction zonewhich is at a temperature at which said reactants will react, theimprovement which comprises introducing at least one of said reactantsinto the zone at a Reynolds number of at least 150,000 wherebysufficient turbulence is created to heat to reaction temperature furtherreactants introduced into said zone and recovering said oxide; thetemperature of said reactants when introduced into said zone being suchthat a mixture thereof does not form a metal oxide, said Reynoldsnumstream of said inlet.

4. The process of claim 3 wherein the reactant at a Reynolds number ofat least 150,000 is introduced into the reaction zone through anorifice, the reaction zone being contained within a reaction chamberhaving a diameter of at least 20 times the diameter of the orifice.

5. The process of producing particulate metal oxide by reaction of avaporous halide selected from the group consisting of chlorides,bromides and iodides of the metal with oxygen, which comprises flowingin a common direction said halide and at least a stoichiometric amountof oxygen to form said metal oxide to a chamber which is at atemperature in excess of 500 C., the temperature of said metal halideand oxygen on introduction to said chamber being such that a mixturethereof does not form said metal oxide and at least one of said halideand oxygen being fed to said chamber in a stream at a Reynolds number inexcess of 50,000, reacting oxygen and said halide in said chamber toform said metal oxide suspended in hot reaction product gases, flowing asuflicient amount of said hot suspension in an opposite direction tosaid common direction whereupon to heat further of said halide andoxygen introduced to said chamber to the temperature of said reaction,and recovering particulate metal oxide from said chamber, said Reynoldsnumber being calculable as the ratio, in consistent units, of four timesthe rate of fluid flow at the reaction zone inlet to the product of thelength of the inside perimeter of said inlet and the fluid viscosityunder the conditions upstream of said inlet.

6. The process of producing pigmentary titanium oxide by reaction ofvaporous titanium tetrachloride with oxygen, which comprises flowing, ina common direction, said titanium tetrachloride and at least astoichiometric amount of oxygen to form titanium oxide to a chamberwhich is at a temperature in excess of 500 C., the temperature of saidtitanium tetrachloride and oxygen on introduction to said chamber beingsuch that a mixture thereof does not form titanium oxide, at least oneof said titanium tetrachloride and oxygen being fed to said chamber in astream at a Reynolds number in excess of 50,000, reacting oxygen andsaid tetrachloride in the chamber to form said titanium oxide suspendedin hot reaction product gases, flowing a sutficient amount of said hotsuspension in an opposite direction to said common direction to heatfurther of said tetrachloride and oxygen introduced to said chamber tothe temperature of said reaction, and recovering pigmentary titaniumoxide from the chamber, said Reynolds number being calculable as theratio, in consistent units, of four times the rate of fluid flow at thereaction zone inlet to the product of the length of the inside perimeterof said inlet and the fluid viscosity under the conditions upstream ofsaid inlet.

7. The process of claim 5 wherein the Reynolds number is in excess of150,000.

8. The process of claim 6 wherein the temperature in the chamber is inexcess of 800 C.

9. In a process for preparing titanium oxide by the exothermic vaporphase reaction of titanium tetrachloride and oxygen, the improvementwhich comprises feeding titanium tetrachloride and oxygen reactants at atemperature such that a mixture thereof is below the temperature ofreaction into a reaction zone chamber, introducing a heat source intosaid chamber to heat the reactants to reaction temperature, at least oneofsaid reactants being fed into the chamber at a Reynolds number above50,000 whereby suflicient turbulence is created to heat to reactiontemperature further of said reactants introduced into said chamber atsaid Reynolds number, and removing the heat source from said chamherwhile continuing the feed of the reactants to said 10 Y chamber at saidnumber, said Reynolds number being calculable as the ratio, inconsistent units, of four times the rate of fluid flow at the reactionzone inlet to the product of the length of the inside perimeter of saidinlet and the fluid viscosity under the conditions upstream of saidinlet.

10. In the process of preparing an oxide by the vapor phase oxidation ofat least one vaporous halide selected from the group consisting of metaland metalloid chlorides, bromides and iodides wherein said halide isreacted with oxygen, the improvement which comprises introducing saidhalide and oxygen at a temperature such that a mixture thereof is belowthe temperature of reaction into a reactor chamber, introducing a heatsource into said reactor chamber to heat the halide and oxygenreact-ants to reaction temperature thereby producing a hot gaseousreaction product mixture comprising an oxide of said halide, at leastone of said reactants being introduced at a Reynolds number of at least50,000 to provide a turbulent body in said chamber thereby heatingfurther of said halide and oxygen to the temperature of re action andremoving the heat source from the chamber .while continuing the feed ofthe reactants to said chamber at said Reynolds number, said Reynoldsnumber being calculable as the ratio, in consistent units, of four timesthe rate of fluid flow at the reaction zone inlet to the product of thelength of the inside perimeter of said inlet and the fluid viscosityunder the conditions upstream of said inlet.

11. In the process of preparing titanium dioxide by the reaction oftitanium tetrachloride with oxygen, the improvement which comprisesfeeding titanium tetrachloride and oxygen reactants in a commondirection into a reactor chamber, interposing an auxiliary flame in thepath of movement of said reactants to react the titanium tetrachlorideWith the oxygen and form a hot reaction mixture, feeding at least one ofsaid reactants into the chamber at a Reynolds number of at least 50,000whereby a cyclic flow of hot reaction mixture to the point of entry ofat least one reactant into the chamber is established, maintaining theflame in operation until suflicient recycling of the reaction mixture isestablished to maintain the reaction, and then extinguishing theauxiliary flame while continuing the feed of the reactants into thechamber, said Reynolds number being calculable as the ratio, inconsistent units, of four times the rate of fluid flow at the reactionzone inlet to the product of the length of the inside perimeter of saidinlet and the fluid viscosity under the conditions upstream of saidinlet.

12. The process of claim 11 wherein at least one reactant is fed intothe chamber at a Reynolds number of at least 150,000.

13. A process of preparing titanium dioxide by the exothermic reactionof titanium tetrachloride and oxygen in the vapor phase which comprisespremixing titanium tetrachloride and at least a stoichiometric amount ofoxygen to form a reactant mixture at a temperature below 500 C.,introducing the reactant mixture through an orifice into a reactionchamber, said chamber having a mean diameter of at least 20 times thediameter of the orifice, establishing an auxiliary flame in the reactionchamber in the path of the reactants to heat the reactants mixture to areaction temperature range of 800 C. to 1200 C. such that there isformed a hot gaseous product mixture containing titanium dioxide, thereactants mixture being introduced to the reaction chamber at a flowrate sufficient to exceed a Reynolds number of at least 150,000 therebyestablishing sufiicient turbulence in said chamber such that the hotgaseous mixture recirculates back toward the reactants mixtureintroduced into the chamber, maintaining the auxiliary flame until asufficient recirculation of the gaseous product mixture is establishedsuch that the reaction of titanium tetrachloride and oxygen isself-sustaining and maintained by its own exothermic heat of reaction,and then withdrawing the auxiliary flame from the reaction chamber whilecontinuing the feed of the reactants mixture to the chamber, saidReynolds number being calculable as the ratio, in consistent units, offour times the rate of fluid flow at the reaction zone inlet to theproduct of the length of the inside perimeter of said inlet and thefluid viscosity under the conditions upstream of said inlet.

14. A process of preparing particulate metallic oxide by the reaction ofa vaporous halide selected from the group consisting of chlorides,bromides and iodides of the metal with oxygen, which comprises flowingsaid halide and oxygen reactants to a chamber which is at a temperaturein excess of 500 C., the temperature of said metal halide and oxygen onintroduction to said chamber being such that a mixture thereof does notform said metal oxide and at least one of said reactants being fed tothe chamber at a Reynolds number in excess of 50,000, reacting saidreactants in said chamber to form as reaction product hot metal oxidesuspended in hot, reaction product gases thereby forming a hot turbulentbody comprising said reaction product which heats further of said halideand oxygen introduced to said chamber to the temperature of reaction,and recovering particulate metal oxide from said chamber, said Reynoldsnumber being calculable as the ratio, in consistent units, of four timesthe rate of fluid flow at the reaction zone inlet to the product of thelength of the inside perimeter of said inlet and the fluid viscosityunder the conditions upstream of said inlet.

15. A process of preparing pigmentary metallic oxide by the vapor phasereaction of at least one metallic halide selected from the groupconsisting of chlorides, bromides and iodides and oxygen which comprisesintroducing the halide and oxygen reactants below the temperature ofreaction into a reactor chamber, supplying auxiliary heat to the chamberin an amount suflicient to initiate the reaction, at least one of saidreactants being introduced through an orifice at a velocity of flowcorresponding to a Reynolds number of at least 50,000, the mean diameterof the chamber being at least 20 times that of the orifice, andterminating the supply of auxiliary heat after the initiation of thereaction, said Reynolds number being calculable as the ratio, inconsistent units, of four times the rate of fluid flow at the reactionzone inlet to the product of the length of the inside perimeter of saidinlet and the fluid viscosity under the conditions upstream of saidinlet.

16. The process of claim 15 wherein at least one reactant is introducedat a Reynolds number of at least 150,000.

References Cited UNITED STATES PATENTS 1,513,622 10/1924 Manning.

1,850,286 3/1932 Mittasch et al 23202 2,395,314 2/1946 Blumer 232192,445,691 7/ 1948 Pechukas 23202 2,791,490 5/1957 Wilcox 23182 X2,855,273 10/1958 Evans et a1.

2,937,928 5/1960 Hughes et a1. 23202 OTHER REFERENCES FluorineChemistry, vol. 1, pp. 3 and 36, by Dr. I. H. Simons, 1950 edition.Academic Press Inc., Publishers, New York, NY.

MILTON WEISSMAN, Primary Examiner.

EDWARD STERN, OSCAR R. VERTIZ, Examiners.

1. IN A PROCESS FOR PREPARING A METALLIC OXIDE BY THE REACTION OF OXYGENWITH AT LEAST ONE OXIDIZABLE, VOLATILE, METALLIC HALIDE SELECTED FROMTHE GROUP CONSISTING OF CHLORIDES, BROMIDES, AND IODIDES, THEIMPROVEMENT WHICH COMPRISES INTRODUCTING THE OXYGEN AND METALLIC HALIDEREACTANTS INTO A REACTION ZONE WHICH IS AT A TEMPERATURE AT WHICH BEINGINTRODUCED INTO THE ZONE AT A REYNOLDS NUMBER OF AT LEAST 50,000 ANDRECOVERING THE RESULTING OXIDE, SAID REYNOLDS NUMBER BEING CALCULABLE ASTHE RATIO, IN CONSISTENT UNITS, OF FOUR TIMES THE RATE OF FLUID FLOW ATTHE REACTION ZONE INLET TO THE PRODUCT OF THE LENGTH OF THE INSIDEPERIMETER OF SAID INLET AND THE FLUID VISCOSITY UNDER THE CONDITIONSUPSTREAM OF SAID INLET.